1. Field of the Invention
The present invention relates generally to mixing of power supplied by multiple power supplies.
2. Description of the Related Art
Fault tolerant computer systems are commonly designed such that component failures occurring in one area of the system are prevented from affecting the remaining areas of the system. Further, fault tolerant computer systems are typically designed to continue operations and maintain data integrity even when a faulty component is being serviced.
Some fault tolerant computer system designs have previously incorporated uninterruptable power supplies (UPSs) to provide the computer system with operating power in the case of a general power outage. UPSs are used externally between the computer system and the general wall power supply, and multiple bulk power supplies are used internally between the UPS and the computer hardware. Having redundant power supplies and power lines ensures that if one bulk power supply is defective, the computer can continue operate from power supplied from another bulk power supply.
In many cases the hardware of a fault tolerant computer system is designed so that when a failure is encountered the user can replace the defective hardware without having to shut the system down, or to call computer service personnel. Replaceable computer hardware are referred to as customer replaceable units (CRUs) or logic units (LU) generally. One problem with allowing customers to replace CRUs is that power to the CRU is often still flowing or "hot" while the computer system is operating. If a CRU is still powered when it is physically removed from the computer housing, damage to the unit, the power supplies, or to other CRUs is possible due, for example, to power surges or electrical arcing across pin connection.